The broad objective of this research project is twofold: (a) To carry out a comparative study of the activity, allosteric characteristics, and post-translational modification of the enzyme phosphofructokinase in muscle and liver of normal and diabetic rabbits in an effort to gain insight into the factors involved in the diminished activity of this key regulatory enzyme in the diabetic state. Several workers reported a block at the glycolytic step catalyzed by phosphofructo-kinase. However, no agreement has been established concerning its causation. (b) To pursue our ongoing investigation on elucidating the amino acid sequence of certain peptides derived from the digestion of phosphofructokinase, e.g., (1) The acetyl carrying peptide (probably it is the N-terminal one); (2) The peptide carrying the activating phosphoryl groups; (3) A peptide at the fructose-6-phosphate site binding site which is to be labeled by an active site oriented analogue; and (4) The peptides resulting from treating rabbit muscle phosphofructokinase with cyanogen bromide. Our long range goal is to determine the complete primary structure of phosphofructokinase and correlate its structure with its mechanism of action and regulation.